This is the incredible moment pop star Katy Perry gatecrashed a wedding reception at the weekend.

The US singing sensation was in St, Louis, Missouri, for a concert as part of her "Witness" world tour when she and "30 to 40" members of her crew made a surprise appearance at the swanky Four Seasons Hotel.

Perry, who turns 33 today, sported a blue jumpsuit, a baseball cap and hoop earrings as she posed for pictures with guests, congratulated the newlyweds and pulled some shapes with the bride on the dancefloor.